This section is intended to introduce the reader to various aspects of art, which may be related to various aspects of the present invention that are described and claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present invention. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.
The loss of computer data can be a serious threat to any business. Backing up computer data is one technique for providing some measure of protection against data loss. One technique for backing up data is to record the data onto magnetic tapes. For example, a magnetic tape configured to operate under the Linear-Tape Open (“LTO”) standard may be used to back-up the data. Under the LTO standard, data is recorded on and read from a moving magnetic tape with an electromagnetic read/write head positioned next to the magnetic tape. Elements within the electromagnetic head are then selectively activated by electric currents which create magnetic flux patterns representing the data on the magnetic tape. The data can then be read from the magnetic tape by moving the electromagnetic tape past the electromagnetic head elements again. In particular, the magnetic flux patterns recorded on the magnetic tape will create electric signals in the electromagnetic head elements, which can be read as the data.
LTO magnetic tapes typically have at least two sections. A first section where the data itself is stored, and a second section that is used to determine the position of the magnetic tape during reading. This second section may contain one or more servo stripes that are tracked by the tape drive to determine the position of the magnetic tape. These servo stripes are recorded on the tape in a repeating pattern during a servo writing process that typically accompanies the manufacture of the magnetic tape. For example, a typical repeating servo stripe pattern includes five right slope (+6 degrees from a direction orthogonal to the direction of the tape's movement) servo stripes, then five left slope (−6 degrees from a direction orthogonal to the direction of the tape's movement) servo stripes, then four right slope servo stripes, then four left slope servo stripes. The position of a head element relative to the tape may be calculated by comparing the time between the first of the five right slope servo stripes and the first of the five left slope servo stripes (referred to as “P time”) with the time between the first of the five right slope servo stripes and the first of the four right slope servo stripes (referred to as “S time”).
In conventional tape servo-write heads, a single coil creates the right slope and left slope servo stripes. This results in servo bands where the P space is fixed or independent of tape speed because it is based on the fixed space between the two stripe writing gaps. In contrast, the S space is variable because it is written at different times and is thus dependent on tape speed and write current timing. Small variations in tape speed during servo writing can be difficult to avoid and can result in a frequency modulation (“FM”) of the S stripes. The presence of this written-in FM in the S stripes may result in position signal noise when the P times are normalized by (e.g., divided by) the S times as position=P time divided by S time This position signal noise can degrade the tracking accuracy of the conventional tape drives.